1. Field of the Invention
The invention relates to a driving device, and more particularly to a light emitting diode (LED) driving device.
2. Description of the Related Art
AC-LEDs can be directly driven with a commercial AC power source. However, referring to FIG. 1, when a current (iac) flowing through an AC-LED increases due to an increased input voltage (vac), a droop effect occurs, thereby resulting in a reduced lighting efficiency. Furthermore, since the AC-LED is sensitive to variation of the input voltage (vac), a small variance in the input voltage (vac) may cause the AC-LED to blink. In addition, since the AC-LED is designed to endure a peak voltage of the input voltage (vac), it has a larger conduction voltage, thereby resulting in lower power factor.
FIG. 2 illustrates a conventional LED driving device disclosed in U.S. Pat. No. 6,989,807. The conventional LED driving device includes a bridge rectifier 30, a current switching circuit 10, a plurality of LEDs, and a voltage detector 20. The bridge rectifier 30 receives and rectifies an AC voltage from a power supply (not shown), and outputs a rectified voltage. The voltage detector 20 controls the current switching circuit 10 based on the rectified voltage from the bridge rectifier 30 to change the number of the LEDs, which are conducted.
However, the current switching circuit 10 has a relatively complex structure, which increases difficulty in current control. There are too many components used in the conventional LED driving device, thereby resulting in a relatively large volume and higher costs.